The influx and efflux of radioactive potassium and chloride across the membrane of the squid giant axon were measured in resting and in stimulated nerves. The measurements were made at room temperature and at 6-8°C. At room temperature all eight flux measurements were comparable to previously reported values. When the axons were cooled the resting potassium influx decreased with a Q10 of 1.9 and the resting potassium efflux decreased with a Q10 of 1.2. With cooling the resting chloride efflux decreased with a Q10 of 1.3 and the resting chloride influx decreased with a Q10 of 2.8. This latter value, together with anomalous flux ratios for resting chloride fluxes may indicate an active uptake of chloride ions into the axon. Cooling increased the extra efflux of potassium associated with nerve impulses with a Q10 of 1/1.5 and increased the extra influx of potassium with a Q10 of 1/3.3. No extra efflux of chloride was detected at either temperature. Cooling produced no statistically significant change in the extra chloride influx but there was considerable scatter in the data. Fluxes were computed as a function of temperature for standard action potentials with a variety of temperature coefficients for the conductances and rate constants. No single curve could match either the influx or the efflux data.
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